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LM27341-Q1 and LM2734Z-Q1

Toshio Ushikubo
Mastermind 9620 points
Other Parts Discussed in Thread: LM27341-Q1, LM2734Z-Q1, LM27341, LM2734Z

I want to use above device for following power supply.

Vin:5.4V to 6.6V
Vout:1.25V/1A


Q1:LM27341-Q1
I calculate "On Time" of following condition using equation(11),(12) of data sheet
and it is 109ns.
 
  Vin:6.6V
  Vout:1.25V
  Fsw:2.3MHz
  Vd1:0.5V
  Rdson:0.15ohm
  Iout:1A   

     -----11

 -----12

LM27341-Q1 data sheet has "Minimum on time:65ns typical", and no maximum value.
So I can't judge if 109 ns is OK or not.
Please advice if I can use LM27341-Q1 for above application.

Q2:LM2734Z-Q1
I calculate "Duty Cycle" of following condition using equation(11),(12),
and it is 25.9%.
 
  Vin:6.6V
  Vout:1.25V
  Fsw:3.6MHz
  Vd1:0.5V
  Rdson:0.34ohm
  Iout:1A
 
LM2734Z-Q1 data sheet has "Minimum Duty Cycle:8% typical", and no maximums value.
So I can't judge if 25.9% is OK or not.
Please advice if I can use LM2734z-Q1 for above application.

Regards.

  • 0
    Mastermind 9620 points

    Hello,

    Please anyone respond my previous questions dated Feb 11 2013.

    Regards.

  • 0 in reply to Toshio Ushikubo
    TI__Genius 15810 points

    Hello Tony,

    This post somehow slipped our radar.

    The LM27341 has a minimum on time of 65ns as you saw in the datasheet. This can be realized as follows:

    ton(min) = Vout/(VinMax*Efficiency*Frequency). Assuming an efficiency of 90%, the resulting ton is about 90ns. This is more than 65ns and therefore this design is possible. You could use Webench to create a design for your requirements.

    The LM2734Z has a maximum duty cycle of 85% (pg. 4 of D/S). Therefore for your requirement the LM2734Z would work. Again, you could use Webench to create a design using this part. The default frequency is 3MHz.

    I hope this information is helpful.

    Regards,
    Akshay 

  • 0 in reply to Akshay Mehta
    Mastermind 9620 points

    Hello Mr. Akshay,

    Thank you for your reply.

    LM27341 Minimum on time 65ns of D/S is typical and D/S does not have maximum value, so I want to

    know haw many margins are required to get safety design.

    For LM2734Z, I have same kind of question. Duty Cycle of my power supply requirement(I already posted)

    is around 29% and it satisfy Maximum Duty Cycle 78%(minimum), but Minimum Duty Cycle pf D/S

    is 9% typical and does not have maximum value.

    How many margins are required against 9% typical of D/S to get safety design?

    Regards.  

  • 0 in reply to Toshio Ushikubo
    TI__Genius 15810 points

    Hello Tony,

    We do not have guaranteed min and max values over temperature. The calculations are all done with the typical value. For your conditions this should not be a problem. I hope this helps.

    Regards,
    Akshay